Method of furnace supervision



0, 1968 w. L. LIVINGSTON 3,369,588

METHOD OF FURNACE SUPERVISION Filed Dec. 7, 1966 INVENTOR WILLIAM L. LlVlNGSTON A ZZM. 6. KW

ATTORNEY United States Patent 3,369,588 METHSD 0F FURNACE SUPERVISION Wiiliam L. Livingston, Sharon, Mass., assignor to Combastion Engineering, Inc, Windsor, Conm, a corporation of Delaware Filed Dec. 7, 1966, Ser. No. 599,939 5 Claims. (Cl. 158117.5)

ABSTRACT OF T333 DISCLDSURE A process of supervising a furnace which is fired with a fuel and air mixture. A stream of gas which may or may not contain unburned fuel is withdrawn from the furnace and is passed through a first zone and a second zone. In each of these zones an attempt is made to ignite the stream. Between these two zones air is introduced into the stream. If ignition occurs in zone 1, the fuel to the furnace is terminated in an inerting medium introduced into the furnace. If ignition occurs in zone 2, the fuel is cut back until such ignition ceases.

Background of the invention There is a continuing search for obtaining safety in the operation of furnaces which are fired with a fuel-air mixture. In furnaces of large capacity safety is obtained by redundancy in the safety equipment, i.e., utilizing several detecting devices principally for detecting the presence or absence of flame. A very dangerous situation exists when the flame is extinguished in the furnace while fuel and air are continued to be supplied to the furnace. Accordingly, it is essential that reliable information be obtained as to the presence or absence of flame in the furnace. Furthermore, it is very desirable to be able to obtain information as to the condition of the flame, particularly as to whether it is fuel-rich, since extinguishing of the flame because of a fuel-rich mixture will produce a dangerous and possibly explosive atmosphere in the furnace when it is attempted to purge the furnace by means of introducing air thereinto as is often done.

With the arrangement of the present invention there is provided an indication as to whether or not an explosive atmosphere exists in the furnace and as to whether or not the fuel-air mixture introduced into the furnace is rich on the fuel side. The invention also provides for control actions to be taken in the event that the furnace atmosphere is explosive or the fuel-air mixture is fuel-rich.

Summary of the invention The atmosphere of the furnace is continuously tested by withdrawing a sample of the atrnosphere from the furnace. The stream produced by thus withdrawing the sample is passed through a first zone wherein there is proided a spark igniter to ignite the sample. If this sample ignites at this zone, the fuel-air mixture is burnable, and accordingly, there is then a dangerous condition existing in the furnace. The presence of burning in this first zone is detected either visually or through automatic detecting means; and when there is burning in this zone, the introduction of fuel into the furnace is terminated and an inerting medium, such as steam, is introduced into the furnace. After passing through this first zone, this sample stream is then introduced into and passed through a second zone. Intermediate these two zones there is introduced into the stream varying quantities of air. In the second zone there is also provided a spark igniter; and if burning takes place in the second zone, there is thus indicated the presence of a fuel-rich mixture in the sample stream. This burning in the second zone is also detected either visually or through automatic means, and the quantity of fuel introduced into the furnace is then decreased until this burning in the second zone ceases. Thus correction of a fuel-rich mixture is provided when necessary and inerting of the furnace is also provided where necessary.

Description of the drawings FIG. 1 discloses, in diagrammatic fashion, a system by means of which the improved operation provided by the invention may be carried out; and

FIG. 2 shows a portion of the system of FIG. 1 in greater detail.

Description of preferred embodiment Referring now to the drawings, wherein like reference characters are used throughout to designate like elements, the illustrative organization shown therein, and by means of which the invention may be carried out, includes a furnace 10 which is supplied with fuel and air for producing a flame therewithin. The fuel is introduced through the fuel supply means 12 and air is introduced via fan 13 and windbox 14 with the air entering the furnace through passage 15. The supply of fuel may be controlled by means of the fuel control valve 16, and the introduction of fuel and air is such as to produce a flammable mixture which is burned within the furnace with the combustion gases passing up through the furnace.

The furnace 10 forms a portion of a steam generator that includes tubes 19 dis-posed along the inner surface of the furnace wall and which, in turn, may be connected to the header or drum 21. For the purpose of inerting the furnace, steam may be directed from this drum 21 through conduit 23 with the steam being introduced into the windbox 14 via the distributor 25. The control of the introduction of this inerting medium is by means of the valve 27. It will be evident that other inerting mediums may be utilized if desired. In the illustrative arrangement there is provided a flame detector 13 which may be any one of a number of conventional types such as an ultraviolet detector as disclosed in US. Patent 3,286,093 of Nov. 15, 1966. This detector may be effective to detect a loss of flame in the furnace and in response to detecting this loss of flame open valve 27 to inert the furnace and simultaneously close valve 16 to shut off the fuel supply.

In accordance with the invention the atmosphere within the furnace is continuously sampled by means of the sampling system identified generally as 20. This sampling system is effective to withdraw a sample of the furnace atmosphere from the furnace at the location 22, and this sample is conveyed through a first zone or chamber 24. Located within this first zone is a spark i-gniter 26 whidh is operated continuously in order to attempt to ignite the stream of gas or gas with intrained solids that passes through this zone. The furnace atmosphere is withdrawn from the furnace through an orifice 23, the purpose of which is to prevent flame from traveling back from said first zone into the furnace and to limit the amount of gas that is withdrawn from the furnace.

The sampling system also includes a second zone .or chamber 27 which likewise includes a spark i-gniter 30. Chambers 24 and 27 may be formed of a suitable glass tube such that the presence of flame therein may be observed. Additionally, there may be associated with these dhambers flame detecting devices of any suitable type with these devices here being identified as 32 and being illustrated in the form of spaced electrodes between which conduction may take place in the presence of a flame. Intermediate zones one and two are provided a means for introducing varying quantities of air in the stream passing through the sampling system. The varying quantity of air is produced by means of the air modulator 34 which is continuously operated to vary the amount of air introduced into the sample stream from a predetermined low to a predetermined high value. This will have the effect of continuously varying the fuel-air mixture passing through, zone two. The sample is caused to pass through the sample system by means of the fan 36, and in the illustrative arrangement the exhaust of this fan is reintroduced into this furnace although it may be discharged to any desirable location.

In operation of the sampling system if ignition occurs in zone one, there is then present in the furnace an atmosphere which is combustible. In suchan instance, the fuel control valve 16is closed and the inertin-g system is activated by opening valve 27. In the event that combustion is produced in zone two, there is provided an indication that there is being introduced into the furnace a fuel-rich mixture such that all of the fuelis not consumed within the furnace. In such instance the supply of fuel is de creased by means of the valve 16 with this decrease being such asto extinguish the flame in zone two.

The control actions thus achieved may be either manual through visual observation of what is taking place in zones one andtwo or may be automatic. The automatic operation can be achieved by means of the flame detectors 32 with there being controllers 40 and 42 associated therewith for obtaiuingthese operations.

Accordingly with the system of the present invention there is provided a supervision of the furnace which will promote the safety of the furnace and tend to prevent the existence within the furnace of an explosive atmosphere. The detection of the presence of a flammable atmosphere in the furnace which will result from the loss of fiame' in the furnace provides a redundant indication to that obtained by the flame detector 18, with redundancy being necessary and desirable in order to provide adequate safeguards.

While I have illustrated and described a preferred embodiment of my invention it is to be understood that.

such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing fromthe spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fallwithin the purview of my invention.

What I claim is:

1. In a furnace into which fuel and air are introduced for burning therewithin the improved process comprising the step of attempting to ignite and burn an unaltered sample of the furnace atmosphere, and the additional step of attempting to then ignite and burn a sample of the furnace atmosphere to which varying quantities. of air are added with the presence or. absence of burning in the first and second mentioned instances being determined.

2. The method of claim 1 wherein the sampling is obtained by continuously withdrawing from the furnace a portion of the atmosphere thereof, conveying the stream thus withdrawn through a first zone wherein the first attempted ignition is effected, thereafter introducing varying quantities of air to this stream and then introducing the stream with the air thus added into a second zone wherein the second-mentioned ignition is attempted.

3. The method of claim 1 including decreasing the fuel introduced into the furnace when ignition and burning takes place in the second instance but not in the first instance with the fuel being decreased until such ignition and burning ceases.

4. The improved method of claim 1 including introducing intothe furnace an inerting medium when ignition and burning takes place in the first instance.

5. An improvedv method of continuously supervising the operation of a furnace comprising introducing fuel and air into the furnace for burning therewithin, continuously sampling thefurnace atmosphere by withdrawing a portion thereof and conveying this portion to a first zone and attempting to ignite the same therein, thereafter introducing into such portion varying quantities of air and passing the portion with the air thus added through a second zone and attempting to ignite the same, terminating the introduction of fuel into the furnace and introducing an inert medium into the furnace in response to burning taking place in said first zone and decreasing the introduction of fuel into the furnace in response to burning taking place insaid second zone with this decreasecontinuing until burning ceases in said second zone.

References Cited UNITED STATES PATENTS 3,192,985 7/1965 Livingston et al. 158-l 3,295,585 3/1967 Kovach et al. 1581l2 FREDERICK L. MATTESON, 111., Primary Examiner.

E. G. .FAVORS, Assistant Examiner. 

